The present invention relates to a contactless data transmission system that is particularly suitable for transmission systems having what are referred to as contactless chip cards. These systems make it possible to exchange data between the chip card and a predominately stationary write/read station for identifying the owner of the card, for effecting a cashless payment, or related purposes.
There are different transmission methods for exchanging data between the chip card and the write/read device. These transmission methods are the subject matter of different partially unfinished standards. Among other things, these standards, such as the ISO/IEC 10536, ISO/IEC 14443 or ISO/IEC 15693, prescribe the data rate of the exchanged data, their coding, the type of modulation, and the carrier frequency of the transmitted signals.
Hitherto, there have been different chip chards and write/read devices, which particularly differ in the maximum permissible distance between the card and the write/read device. Systems for the xe2x80x9cproximity rangexe2x80x9d function up to distances of approximately 10 cm, while systems for the xe2x80x9cvicinity rangexe2x80x9d function up to a distance of approximately 1 m.
International publication WO 96/29673 discloses a transponder for a chip card. From the properties of the received electromagnetic wave, the transponder determines the standard with which the write-read device works. The transponder is adjusted with respect to the recognized standard. The stereo effect is used for recognizing whether the transponder is situated in the proximity field or the vicinity field.
A disadvantage of this known system is that while, the transponder can be operated by using a number of standards, the standard that is most suitable for the transponder is not taken into consideration.
It is accordingly an object of the invention to provide a contactless data transmission system and a method for operating the system which overcomes the above-mentioned disadvantageous of the prior art apparatus and methods of this general type. In particular, it is an object of the invention to provide a contactless data transmission device having a transponder, whereby the standard that is suitable for the transponder can be selected.
With the foregoing and other objects in view there is provided, in accordance with the invention, a contactless data transmission system that includes a transponder; and a write/read station for generating HF signals to exchange data with the transponder. The transponder includes a reception unit including a receiving interface for receiving the HF signals generated by the write/read station and for thereby obtaining received HF signals. The reception unit has an output terminal for providing data signals that are formed from the received HF signals. The reception unit includes a device for receiving and processing at least two signals selected from the group consisting of differently modulated ones of the received HF signals and differently encoded ones of the received HF signals. The transponder also includes a processing unit including a first input terminal that is connected to the output terminal of the reception unit. The transponder also includes a detection unit for providing a control signal dependent on the performance of the received HF signal. The transponder also includes a transmission unit that is driven dependent on the control signal. The transmission unit is for generating a HF signal that is selected from the group consisting of a signal that is modulated in a first manner, a signal that is modulated in a second manner, a signal that is encoded in a first manner, and a signal that is encoded in a second manner. A unit that is selected from the group consisting of the reception unit and the processing unit is driven dependent on the control signal.
In other words, the transponder or, respectively, the chip card of the transmission system has a reception unit with a receiving interface for receiving a HF signal transmitted by the write/read station. The reception unit has an output terminal for providing a data signal formed in the reception unit from the HF signal. The reception unit has means for receiving and processing HF signals that are differently modulated and/or encoded. The reception unit is particularly appropriate for receiving, demodulating and decoding HF signals, which have been produced and transmitted according to one or more of the already existing transmission standards. The reception unit is followed by a processing unit for processing the data signal acquired from the HF signal.
Furthermore, the transponder has a detector unit for providing a control signal that is dependent on the performance of the received HF signal. The reception unit and/or the processing unit can be driven by the control signal. The control signal has information about the performance of the received HF signal and therefore about the distance of the chip card from the write/read station. Dependent on the intensity of the received HF signal, the transponder of the inventive transmission system enables the reception unit and/or the processing unit to be adjusted to the transmission method that is optimal for the determined distance between the chip card and the write/read device.
In accordance with an added feature of the invention, the transponder has a transmission unit, which is connected to the processing unit and which has means for generating at least two differently modulated and/or encoded HF signals from a data signal supplied by the processing unit. The transmission unit can be preferably driven dependent on the control signal for generating differently modulated and/or encoded HF signals, which belong to different transmission standards.
If during a data transmission that is based on a first transmission method which requires a small distance between the chip card and the write/read device, for example as a result of a high data rate, the user moves away from the read/write device, then by changing over to another transmission method, which still securely functions even with respect to larger distances, the started data transmission can be completed or at least can be interrupted without data loss.
The modulation methods and encoding methods used by the reception unit and the transmission unit are particularly based on transmission standards, which have been created for different distances between the chip card and the write/read device. These standards are particularly different with respect to the data rate, which is greater for the proximity range (according to ISO 1443) than for the vicinity range (according to ISO 15693).
In accordance with an additional feature of the invention, the detection unit is connected directly to the reception unit in order to drive the reception unit in dependence on the control signal. In another embodiment, the detection unit is connected to the processing unit and the reception unit is connected to the processing unit in order to drive the reception unit dependent on the control signal via the processing unit. This embodiment has the advantage that the processing unit recognizes from the control signal whether it is necessary to change the transmission method, since the chip card has been removed from the write/read device, for example. Alternatively, the processing unit can recognize that it is possible to change over to a transmission method having a higher data rate, since the chip card has been further approximated to the write/read device. Subsequently, the processing unit can adapt the transmission unit and the reception unit to the modified requirements and the respective transmission method according to the processing of the received data signal and the data to be transmitted to the write/read station. This embodiment has the additional advantage that further parameters, which make a change of the transmission method appear necessary, can be considered in the processing unit in addition to the control signal.
In accordance with another feature of the invention, the reception unit preferably has at least two signal processing units for receiving and processing two differently modulated and/or encoded HF signals. The signal processing units each have a receiver, a demodulator and a decoder. Dependent on how the HF signals to be processed differ, the signal processing units can have one or more of the components in common. For example, if the HF signals differ only with respect to the type of modulation and encoding but not with respect to the carrier frequency, one receiver that is tuned to the carrier frequency and that can be common to both signal processing units is sufficient. If the two signals differ only with respect to their encoding, the receiver and demodulator can be used together.
In accordance with a further feature of the invention, for adjusting the reception unit to the processing of one of the possible HF signals, the components of the signal processing units preferably can be individually driven dependent on the control signal. The components that are not needed are preferably switched off in order so save current.
In accordance with a further added feature of the invention, for generating the control signal, the detection unit is preferably connected to an output terminal of the reception unit. In addition to the means for demodulating and decoding the HF signals, the reception unit has a voltage supply unit with a voltage regulator, which provides a supply voltage for the switching components of the transponder by rectifying and smoothing the HF signal. A voltage regulator serves the purpose of maintaining an at least approximately constant supply voltage. Voltage fluctuations as a result of a powerful HF signal are adjusted by the voltage regulator. Therefore, the voltage regulator has information about the performance of the received HF signal. The information can be supplied to the detection unit for forming the control signal (as is provided in an embodiment of the invention).
In accordance with a further additional feature of the invention, the write/read device has means for receiving a signal transmitted by the transponder and for changing the transmission method dependent on the received signal. The write/read device of the inventive transmission system preferably has a configuration, which corresponds to the transponder and includes a reception unit, a processing unit and a transmission unit. This reception unit has means for receiving and processing HF signals, which are modulated and/or encoded in at least two different ways. The transmission unit preferably has means for generating corresponding differently modulated and/or encoded HF signals.
In accordance with yet an added feature of the invention, in a further embodiment of the invention, the write/read device has means for determining an error rate of the signals received by the transponder and has means for changing the transmission method dependent on the error rate.
In accordance with yet an additional feature of the invention, the transponder of the inventive system also can be operated in connection with a write/read device that does not have all of transmission methods implemented that are implemented in the transponder. As a result, however, it is not possible to switch between all of the transmission methods that are possible for the transponder. The processing unit of the transponder is preferably fashioned such that it only allows a changeover to such a transmission method for which a corresponding request signal is received by the write/read device.
With the foregoing and other objects in view there is also provided, in accordance with the invention, a process for operating the above-described transmission system. In the process, a transmission method is initially adjusted in the system at the beginning of the transmission, when the processing unit is charged with the supply voltage. The transmission method functions reliably also regarding larger distances between the transponder and the chip card, and provides that the transmission method is subsequently adjusted dependent on the control signal.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a contactless data transmission system and method for the contactless data transmission, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.